Since the sub-office has been established in the Bourse, it has been made a distributing as well as receiving office. At least two more deliveries of mail are made each day in the Bourse building than in any other office building in the city. All letters mailed in the sub-office with a special delivery stamp are despatched through the tube immediately. It is now nearly four years since the system was put into operation. During that time more than thirty-five million letters have been transported, and all the repairs to the system have not required it to be stopped for more than a few hours. During the first year the Pneumatic Transit Company operated the tubes at their own expense, agreeing at the end of that time to take them out if the government so requested. Since the first year the government has paid the running expenses. Such is the history of the first United States pneumatic postal system. Such is the history of the first pneumatic tubes of sufficient size to carry all the first class and most of the lower classes of mail, in this or any other country, so far as the writer knows. CHAPTER III. THE SYSTEM AND APPARATUS OF THE BATCHELLER PNEUMATIC TUBE COMPANY. =General Arrangement and Adaptability of the System.=—The experience gained in the construction and operation of the Philadelphia post-office tubes has naturally suggested improvements that can be made in future construction, and, furthermore, it has taught us what the requirements will be of an extensive system of tubes laid in the streets of our cities, both for the transmission of mail and for a general commercial business. Since the Philadelphia post-office tube was completed, we have been busily engaged in working out all the details of a system of many stations so connected together that carriers can be despatched in the most direct manner possible from any station to any other. It is the purpose of the present chapter to describe this system. While the Pneumatic Transit Company has ample field in the State of Pennsylvania to carry out the work which it has mapped out, a field broad enough to yield a good profit for the capital invested, there is no reason why the system should be limited to one State. So, in order to obtain a broader charter, covering all places where pneumatic service may be needed, a new corporation was formed and styled the BATCHELLER PNEUMATIC TUBE COMPANY.